1. Field of the Invention
This invention relates to devices for venting outside air along the underside of roof sheathing to a point above the attic insulation layer.
2. Description of the Prior Art
It is well known in the prior art that a flow of air on the underside of roof sheathing will improve insulation efficiency and reduce the buildup of moisture in insulating material. Circulating air also helps prevent ice dams on the roof. An ice dam develops when water flows from a warm area of a roof down to a colder area where it freezes. As more water freezes, a dam develops which prevents water from flowing past the point. This water can back up under shingles and leak into the attic. It can then soak into insulation and decrease its efficiency. It can also leak into the interior of the building and cause structural and cosmetic damage. One cause of such damming is heat moving through the roof to melt ice. The water melted from the ice then flows down to form a dam at a lower, colder place. It is known that cool outside air circulating under the roof sheathing helps to prevent such ice melting.
The Uniform Building Code Section 320.5 requires venting along the underside of roof sheathing.
Many types of devices have been developed which allow air circulation under the roof sheathing. It is also known in the prior art to mold one piece, closed cell, expanded polystyrene vents which can be applied to roof sheathing to form an air channel from under the eave to a point in the attic above a level of insulation. In the prior art, these one piece polystyrene vents were nailed or stapled to the roof sheathing. This resulted in many damaged or destroyed vents because of errant blows of a hammer or stapler. Once cracked, a vent can become useless, if, during installation, insulation is blown or otherwise forced up into the vent. This will block air flow.
Polystyrene vents in the prior art including flat panels parallel to the roof sheathing also suffered damage and reduction of air space when insulation forced in the attic area below them bowed the bottom surface of the vent upward. Polystyrene is a preferred material for such a vent because it provides insulation as well as an air barrier. A flat polystyrene panel is not strong enough, however, to withstand the pressure of insulation blown or otherwise forced against it.